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  • Collision rectangle response

    - by dotty
    I'm having difficulties getting a moveable rectangle to collide with more than one rectangle. I'm using SFML and it has a handy function called Intersect() which takes 2 rectangles and returns the intersections. I have a vector full of rectangles which I want my moveable rectangle to collide with. I'm looping through this using the following code (p is the moveble rectangle). IsCollidingWith returns a bool but also uses SFML's Interesect to work out the intersections. while(unsigned i = 0; i!= testRects.size(); i++){ if(p.IsCollidingWith(testRects[i]){ p.Collide(testRects[i]); } } and the actual Collide() code void gameObj::collide( gameObj collidingObject ){ printf("%f %f\n", this->colliderResult.width, this->colliderResult.height); if (this->colliderResult.width < this->colliderResult.height) { // collided on X if (this->getCollider().left < collidingObject.getCollider().left ) { this->move( -this->colliderResult.width , 0); }else { this->move( this->colliderResult.width, 0 ); } } if(this->colliderResult.width > this->colliderResult.height){ if (this->getCollider().top < collidingObject.getCollider().top ) { this->move( 0, -this->colliderResult.height); }else { this->move( 0, this->colliderResult.height ); } } } and the IsCollidingWith() code is bool gameObj::isCollidingWith( gameObj testObject ){ if (this->getCollider().intersects( testObject.getCollider(), this->colliderResult )) { return true; }else { return false; } } This works fine when there's only 1 Rect in the scene. However, when there's move than one Rect it causes issue when working out 2 collisions at once. Any idea how to deal with this correctly? I have uploaded a video to youtube to show my problem. The console on the far-right shows the width and height of the intersections. You can see on the console that it's trying to calculate 2 collisions at once, I think this is where the problem is being caused. The youtube video is at http://www.youtube.com/watch?v=fA2gflOMcAk also , this image also seems to illustrate the problem nicely. Can someone please help, I've been stuck on this all weekend!

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  • Collision Detection Problems

    - by MrPlosion
    So I'm making a 2D tile based game but I can't quite get the collisions working properly. I've taken the code from the Platformer Sample and implemented it into my game as seen below. One problem I'm having is when I'm on the ground for some strange reason I can't move to the left. Now I'm pretty sure this problem is from the HandleCollisions() method because when I stop running it I can smoothly move around with no problems. Another problem I'm having is when I'm close to a tile the character jitters very strangely. I will try to post a video if necessary. Here is the HandleCollisions() method: Thanks. void HandleCollisions() { Rectangle bounds = BoundingRectangle; int topTile = (int)Math.Floor((float)bounds.Top / World.PixelTileSize); int bottomTile = (int)Math.Ceiling((float)bounds.Bottom / World.PixelTileSize) - 1; int leftTile = (int)Math.Floor((float)bounds.Left / World.PixelTileSize); int rightTile = (int)Math.Ceiling((float)bounds.Right / World.PixelTileSize) - 1; isOnGround = false; for(int x = leftTile; x <= rightTile; x++) { for(int y = topTile; y <= bottomTile; y++) { if(world.Map[y, x].Collidable == true) { Rectangle tileBounds = new Rectangle(x * World.PixelTileSize, y * World.PixelTileSize, World.PixelTileSize, World.PixelTileSize); Vector2 depth = RectangleExtensions.GetIntersectionDepth(bounds, tileBounds); if(depth != Vector2.Zero) { if(Math.Abs(depth.Y) < Math.Abs(depth.X)) { isOnGround = true; position = new Vector2(position.X, position.Y + depth.Y); } else { position = new Vector2(position.X + depth.X, position.Y); } bounds = BoundingRectangle; } } } }

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  • Collision Detection within Player/Enemy Class

    - by user1264811
    I'm making a 2D platform game. Right now I'm just working on making a very generic Player class. I'm wondering if it would be more efficient/better practice to have an ActionListener within the Player class to detect collisions with Enemy objects (also have an ActionListener) or to handle all the collisions in the main world. Furthermore, I'm thinking ahead about how I will handle collisions with the platforms themselves. I've looked into the double boolean arrays to see which tiles players can go to and which they can't. I don't understand how to use this class and the player class at the same time. Thank you.

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  • Why is my collision detection not accurate?

    - by optimisez
    After trying and trying, I still cannot understand why the leg of character exceeds the wall but no clipping issue when I hit the wall from below. How should I fix it to make him stand still on the wall? From collideWithBox() function below, it shows that playerDest.Y = boxDest.Y - boxDest.height; will get the position the character should standstill on the wall. Theoretically, the clipping effect won't be happen as the character hit the box from below works with the equation playerDest.Y = boxDest.Y + boxDest.height;. void collideWithBox() { if ( spriteCollide(playerDest, boxDest) && keyArr[VK_UP]) //playerDest.Y += 50; playerDest.Y = boxDest.Y + boxDest.height; else if ( spriteCollide(playerDest, boxDest) && !keyArr[VK_UP]) playerDest.Y = boxDest.Y - boxDest.height; } void initPlayer() { // Create texture. hr = D3DXCreateTextureFromFileEx(d3dDevice, "player.png", 169, 44, D3DX_DEFAULT, NULL, D3DFMT_A8R8G8B8, D3DPOOL_MANAGED, D3DX_DEFAULT, D3DX_DEFAULT, D3DCOLOR_XRGB(255, 255, 255), NULL, NULL, &player); playerRect.left = playerRect.top = 0; playerRect.right = 29; playerRect.bottom = 36; playerDest.X = 0; playerDest.Y = 564; playerDest.length = playerRect.right - playerRect.left; playerDest.height = playerRect.bottom - playerRect.top; } void initBox() { hr = D3DXCreateTextureFromFileEx(d3dDevice, "brock.png", 330, 132, D3DX_DEFAULT, NULL, D3DFMT_A8R8G8B8, D3DPOOL_MANAGED, D3DX_DEFAULT, D3DX_DEFAULT, D3DCOLOR_XRGB(255, 255, 255), NULL, NULL, &box); boxRect.left = 33; boxRect.top = 0; boxRect.right = 63; boxRect.bottom = 30; boxDest.X = boxDest.Y = 300; boxDest.length = boxRect.right - boxRect.left; boxDest.height = boxRect.bottom - boxRect.top; } bool spriteCollide(Entity player, Entity target) { float left1, left2; float right1, right2; float top1, top2; float bottom1, bottom2; left1 = player.X; left2 = target.X; right1 = player.X + player.length; right2 = target.X + target.length; top1 = player.Y; top2 = target.Y; bottom1 = player.Y + player.height; bottom2 = target.Y + target.height; if (bottom1 < top2) return false; if (top1 > bottom2) return false; if (right1 < left2) return false; if (left1 > right2) return false; return true; }

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  • Bitmap & Object Collision Help

    - by MarkEz
    Is it possible to detect when an object and a bitmap collide. I have an arraylist of sprites that I am shooting with an image. I tried using this method here but as soon as the bitmap appears the sprite disappears, this is in the Sprite class: public boolean isCollision(Bitmap other) { // TODO Auto-generated method stub if(other.getWidth() > x && other.getWidth() < x + width && >other.getHeight() > y && other.getHeight() < y + height); return true; }

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  • Bitmap & Object Collision Help

    - by MarkEz
    Is it possible to detect when an object and a bitmap collide. I have an arraylist of sprites that I am shooting with an image. I tried using this method here but as soon as the bitmap appears the sprite disappears, this is in the Sprite class: public boolean isCollision(Bitmap other) { if(other.getWidth() > x && other.getWidth() < x + width && >other.getHeight() > y && other.getHeight() < y + height); return true; }

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  • Elastic Collision Formula in Java

    - by Shijima
    I'm trying to write a Java formula based on this tutorial: 2-D elastic collisions without Trigonometry. I am in the section "Elastic Collisions in 2 Dimensions". In step 1, it mentions "Next, find the unit vector of n, which we will call un. This is done by dividing by the magnitude of n". My below code represents the normal vector of 2 objects (I'm using a simple array to represent the normal vector), but I am not really sure what the tutorial means by dividing the magnitude of n to get the un. int[] normal = new int[2]; normal[0] = ball2.x - ball1.x; normal[1] = ball2.y - ball1.y; Can anyone please explain what un is, and how I can calculate it with my array in Java?

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  • SAT and then what?

    - by Marek
    I am on my way to make another Arkanoid game but this time I decided that I want it a little bit more realistic than just checking intersections between AABB and inverting one vector's component on collision. So I found SAT but I don't know how can I change direction of the ball in realistic matter. Maybe I'm wrong but it seems like knowing MTV doesn't give me much. So my question is what algorithms should I use to make it realistic? I also care about possibility of spinning ball with a pallet. I don't know how to do it exactly but I guess I will need to consider acceleration of the pallet.

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  • Collisions between moving ball and polygons

    - by miguelSantirso
    I know this is a very typical problem and that there area a lot of similar questions, but I have been looking for a while and I have not found anything that fits what I want. I am developing a 2D game in which I need to perform collisions between a ball and simple polygons. The polygons are defined as an array of vertices. I have implemented the collisions with the bounding boxes of the polygons (that was easy) and I need to refine that collision in the cases where the ball collides with the bounding box. The ball can move quite fast and the polygons are not too big so I need to perform continuous collisions. I am looking for a method that allows me to detect if the ball collides with a polygon and, at the same time, calculate the new direction for the ball after bouncing in the polygon. (I am using XNA, in case that helps)

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  • Meaning of offset in pygame Mask.overlap methods

    - by Alan
    I have a situation in which two rectangles collide, and I have to detect how much did they collide so so I can redraw the objects in a way that they are only touching each others edges. It's a situation in which a moving ball should hit a completely unmovable wall and instantly stop moving. Since the ball sometimes moves multiple pixels per screen refresh, it it possible that it enters the wall with more that half its surface when the collision is detected, in which case i want to shift it position back to the point where it only touches the edges of the wall. Here is the conceptual image it: I decided to implement this with masks, and thought that i could supply the masks of both objects (wall and ball) and get the surface (as a square) of their intersection. However, there is also the offset parameter which i don't understand. Here are the docs for the method: Mask.overlap Returns the point of intersection if the masks overlap with the given offset - or None if it does not overlap. Mask.overlap(othermask, offset) -> x,y The overlap tests uses the following offsets (which may be negative): +----+----------.. |A | yoffset | +-+----------.. +--|B |xoffset | | : :

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  • How to make it so units don't stack up in one location?

    - by Daggio
    So I'm making a game in AS3, it's a strategy DotA-like game (for flash game equivalent, there's UDE) so far so good, I have the A* pathfinding algorithm all sorted out and the minion units move to the desired location as I want them to be. The problem a rise when a unit stops in a node that has already occupied by another friendly unit. Both (or more than two) of them stacks up in one location, it looks like they're one unit. I want to add collision detection so when they collide they don't stack up together. But now they stop when they collide on they way to a node. This isn't good because they won't move at all midway (they won't respond to enemy attacks like that). I've added a deltatime so they only stopped for 2 seconds before they move again to their designated designation. This moves them again but they flicker. Not how I want it. So, like the title said. How to make more than one units don't stack up in a node? And if possible, how to make them not flicker while moving (it's good if they can tell other friendly units on the way and avoid them accordingly)?

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  • Simulating smooth movement along a line after calculating a collision containing a restitution of zero in 2D

    - by Casey
    [for tl;dr see after listing] //...Code to determine shapes types involved in collision here... //...Rectangle-Line collision detected. if(_rbTest->GetCollisionShape()->Intersects(*_ground->GetCollisionShape())) { //Convert incoming shape to a line. a2de::Line l(*dynamic_cast<a2de::Line*>(_ground->GetCollisionShape())); //Get line's normal. a2de::Vector2D normal_vector(l.GetSlope().GetY(), -l.GetSlope().GetX()); a2de::Vector2D::Normalize(normal_vector); //Accumulate forces involved. a2de::Vector2D intermediate_forces; a2de::Vector2D normal_force = normal_vector * _rbTest->GetMass() * _world->GetGravityHandler()->GetGravityValue(); intermediate_forces += normal_force; //Calculate final velocity: See [1] double Ma = _rbTest->GetMass(); a2de::Vector2D Ua = _rbTest->GetVelocity(); double Mb = _ground->GetMass(); a2de::Vector2D Ub = _ground->GetVelocity(); double mCr = Mb * _ground->GetRestitution(); a2de::Vector2D collision_velocity( ((Ma * Ua) + (Mb * Ub) + ((mCr * Ub) - (mCr * Ua))) / (Ma + Mb)); //Calculate reflection vector: See [2] a2de::Vector2D reflect_velocity( -collision_velocity + 2 * (a2de::Vector2D::DotProduct(collision_velocity, normal_vector)) * normal_vector ); //Affect velocity to account for restitution of colliding bodies. reflect_velocity *= (_ground->GetRestitution() * _rbTest->GetRestitution()); _rbTest->SetVelocity(reflect_velocity); //THE ULTIMATE ISSUE STEMS FROM THE FOLLOWING LINE: //Move object away from collision one pixel to prevent constant collision. _rbTest->SetPosition(_rbTest->GetPosition() + normal_vector); _rbTest->ApplyImpulse(intermediate_forces); } Sources: (1) Wikipedia: Coefficient of Restitution: Speeds after impact (2) Wikipedia: Specular Reflection: Direction of reflection First, I have a system in place to account for friction (that is, a coefficient of friction) but is not used right now (in addition, it is zero, which should not affect the math anyway). I'll deal with that after I get this working. Anyway, when the restitution of either object involved in the collision is zero the object stops as required, but if movement along the same direction (again, irrespective of the friction value that isn't used) as the line is attempted the object moves as if slogging through knee deep snow. If I remove the line of code in question and the object is not push away one pixel the object barely moves at all. All because the object collides, is stopped, is pushed up, collides, is stopped...etc. OR collides, is stopped, collides, is stopped, etc... TL;DR How do I only account for a collision ONCE for restitution purposes (BONUS: but CONTINUALLY for frictional purposes, to be implemented later)

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  • How to avoid tons of `instanceof` in collision detection?

    - by Prog
    Consider a simple game with 4 kinds of entities: Robots, Dogs, Missiles, Walls. Here's a simple collision-detection mechanism in psuedocode: (I know, O(n^2). Irrelevant for this question). for(Entity entityA in entities){ for(Entity entityB in entities){ if(collision(entityA, entityB)){ if(entityA instanceof Robot && entityB instanceof Dog) entityB.die(); if(entityA instanceof Robot && entityB instanceof Missile){ entityA.die(); entityB.die(); } if(entityA instanceof Missile && entityB instanceof Wall) entityB.die(); // .. and so on } } } Obviously this is very ugly, and will get bigger and harder to maintain the more entities there are, and the more conditions there are. One option to make this better is to have separate lists for each kind of entity. For example a Robots list, a Dogs list etc. And than check for collisions of all Robots with Dogs, and all Dogs with Walls, etc. This is better, but I still don't think it's good. So my question is: The collision detection system spotted a collision. Now what? What is the common way to react to the collision? Should the system notify the entity itself that it collided with something, and have it decide for itself how to react? E.g. entityA.reactToCollision(entityB). Or is there some other solution?

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  • Mass Ball-to-Ball Collision Handling (as in, lots of balls)

    - by BlueThen
    Update: Found out that I was using the radius as the diameter, which was why the mtd was overcompensating. Hi, StackOverflow. I've written a Processing program awhile back simulating ball physics. Basically, I have a large number of balls (1000), with gravity turned on. Detection works great, but my issue is that they start acting weird when they're bouncing against other balls in all directions. I'm pretty confident this involves the handling. For the most part, I'm using Jay Conrod's code. One part that's different is if (distance > 1.0) return; which I've changed to if (distance < 1.0) return; because the collision wasn't even being performed with the first bit of code, I'm guessing that's a typo. The balls overlap when I use his code, which isn't what I was looking for. My attempt to fix it was to move the balls to the edge of each other: float angle = atan2(y - collider.y, x - collider.x); float distance = dist(x,y, balls[ID2].x,balls[ID2].y); x = collider.x + radius * cos(angle); y = collider.y + radius * sin(angle); This isn't correct, I'm pretty sure of that. I tried the correction algorithm in the previous ball-to-ball topic: // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); except my version doesn't use vectors, and every ball's weight is 1. The resulting code I get is this: PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.5; y -= mtd.y * 0.5; collider.x += mtd.x * 0.5; collider.y += mtd.y * 0.5; This code seems to over-correct collisions. Which doesn't make sense to me because in no other way do I modify the x and y values of each ball, other than this. Some other part of my code could be wrong, but I don't know. Here's the snippet of the entire ball-to-ball collision handling I'm using: if (alreadyCollided.contains(new Integer(ID2))) // if the ball has already collided with this, then we don't need to reperform the collision algorithm return; Ball collider = (Ball) objects.get(ID2); PVector collision = new PVector(x - collider.x, y - collider.y); float distance = collision.mag(); if (distance == 0) { collision = new PVector(1,0); distance = 1; } if (distance < 1) return; PVector velocity = new PVector(vx,vy); PVector velocity2 = new PVector(collider.vx, collider.vy); collision.div(distance); // normalize the distance float aci = velocity.dot(collision); float bci = velocity2.dot(collision); float acf = bci; float bcf = aci; vx += (acf - aci) * collision.x; vy += (acf - aci) * collision.y; collider.vx += (bcf - bci) * collision.x; collider.vy += (bcf - bci) * collision.y; alreadyCollided.add(new Integer(ID2)); collider.alreadyCollided.add(new Integer(ID)); PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.2; y -= mtd.y * 0.2; collider.x += mtd.x * 0.2; collider.y += mtd.y * 0.2; Thanks. (Apologies for lack of sources, stackoverflow thinks I'm a spammer)

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  • how get collision callback of two specific objects using bullet physics?

    - by sebap123
    I have got problem implementing collision callback into my project. I would like to have detection between two specific objects. I have got normall collision but I want one object to stop or change color or whatever when colides with another. I wrote code from bullet wiki: int numManifolds = dynamicsWorld->getDispatcher()->getNumManifolds(); for (int i=0;i<numManifolds;i++) { btPersistentManifold* contactManifold = dynamicsWorld->getDispatcher()->getManifoldByIndexInternal(i); btCollisionObject* obA = static_cast<btCollisionObject*>(contactManifold->getBody0()); btCollisionObject* obB = static_cast<btCollisionObject*>(contactManifold->getBody1()); int numContacts = contactManifold->getNumContacts(); for (int j=0;j<numContacts;j++) { btManifoldPoint& pt = contactManifold->getContactPoint(j); if (pt.getDistance()<0.f) { const btVector3& ptA = pt.getPositionWorldOnA(); const btVector3& ptB = pt.getPositionWorldOnB(); const btVector3& normalOnB = pt.m_normalWorldOnB; bool x = (ContactProcessedCallback)(pt,fallRigidBody,earthRigidBody); if(x) printf("collision\n"); } } } where fallRigidBody is a dynamic body - a sphere and earthRigiBody is static body - StaticPlaneShape and sphere isn't touching earthRigidBody all the time. I have got also other objects that are colliding with sphere and it works fine. But the program detects collision all the time. It doesn't matter if the objects are or aren't colliding. I have also added after declarations of rigid body: earthRigidBody->setCollisionFlags(earthRigidBody->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK); fallRigidBody->setCollisionFlags(fallRigidBody->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK); So can someone tell me what I am doing wrong? Maybe it is something simple?

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  • Breakout clone, how to handle/design for collision detection/physics between objects?

    - by Zolomon
    I'm working on a breakout clone, and I wish to create some realistic physics effects for collision - angles on the paddle should allow the ball to bounce, as well as doing curve balls etc. I could use per-pixel based collision detection, but then I thought it might be easier with line/circle intersection testing. So, then I naturally consider making a polygon class for the line-based objects and use the built-in circle class for the circular objects. That sounds like an OK approach, right? And then just check for collision using the specified algorithm based on the objects that might be within each other's range?

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  • Is there a good way to get pixel-perfect collision detection in XNA?

    - by ashes999
    Is there a well-known way (or perhaps reusable bit of code) for pixel-perfect collision detection in XNA? I assume this would also use polygons (boxes/triangles/circles) for a first-pass, quick-test for collisions, and if that test indicated a collision, it would then search for a per-pixel collision. This can be complicated, because we have to account for scale, rotation, and transparency. WARNING: If you're using the sample code from the link from the answer below, be aware that the scaling of the matrix is commented out for good reason. You don't need to uncomment it out to get scaling to work.

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  • How can I get accurate collision resolution on the corners of rectangles?

    - by ssb
    I have a working collision system implemented, and it's based on minimum translation vectors. This works fine in most cases except when the minimum translation vector is not actually in the direction of the collision. For example: When a rectangle is on the far edge on any side of another rectangle, a force can be applied, in this example down, the pushes one rectangle into the other, particularly a static object like a wall or a floor. As in the picture, the collision is coming from above, but because it's on the very edge, it translates to the left instead of back up. I've searched for a while to find an approach but everything I can find deals with general corner collisions where my problem is only in this one limited case. Any suggestions?

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  • Without using a pre-built physics engine, how can I implement 3-D collision detection from scratch?

    - by Andy Harglesis
    I want to tackle some basic 3-D collision detection and was wondering how engines handle this and give you a pretty interface and make it so easy ... I want to do it all myself, however. 2-D collision detection is extremely simple and can be done multiple ways that even beginner programmers could think up: 1.When the pixels touch; 2.when a rectangle range is exceeded; 3.when a pixel object is detected near another one in a pixel-based rendering engine. But 3-D is different with one dimension, but complex in many more so ... what are the general, basic understanding/examples on how 3-D collision detection can be implemented? Think two shaded, OpenGL cubes that are moved next to each other with a simple OpenGL rendering context and keyboard events.

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  • Ball to Ball Collision - Detection and Handling

    - by Simucal
    With the help of the Stack Overflow community I've written a pretty basic-but fun physics simulator. You click and drag the mouse to launch a ball. It will bounce around and eventually stop on the "floor". My next big feature I want to add in is ball to ball collision. The ball's movement is broken up into a x and y speed vector. I have gravity (small reduction of the y vector each step), I have friction (small reduction of both vectors each collision with a wall). The balls honestly move around in a surprisingly realistic way. I guess my question has two parts: What is the best method to detect ball to ball collision? Do I just have an O(n^2) loop that iterates over each ball and checks every other ball to see if it's radius overlaps? What equations do I use to handle the ball to ball collisions? Physics 101 How does it effect the two balls speed x/y vectors? What is the resulting direction the two balls head off in? How do I apply this to each ball? Handling the collision detection of the "walls" and the resulting vector changes were easy but I see more complications with ball-ball collisions. With walls I simply had to take the negative of the appropriate x or y vector and off it would go in the correct direction. With balls I don't think it is that way. Some quick clarifications: for simplicity I'm ok with a perfectly elastic collision for now, also all my balls have the same mass right now, but I might change that in the future. In case anyone is interested in playing with the simulator I have made so far, I've uploaded the source here (EDIT: Check the updated source below). Edit: Resources I have found useful 2d Ball physics with vectors: 2-Dimensional Collisions Without Trigonometry.pdf 2d Ball collision detection example: Adding Collision Detection Success! I have the ball collision detection and response working great! Relevant code: Collision Detection: for (int i = 0; i < ballCount; i++) { for (int j = i + 1; j < ballCount; j++) { if (balls[i].colliding(balls[j])) { balls[i].resolveCollision(balls[j]); } } } This will check for collisions between every ball but skip redundant checks (if you have to check if ball 1 collides with ball 2 then you don't need to check if ball 2 collides with ball 1. Also, it skips checking for collisions with itself). Then, in my ball class I have my colliding() and resolveCollision() methods: public boolean colliding(Ball ball) { float xd = position.getX() - ball.position.getX(); float yd = position.getY() - ball.position.getY(); float sumRadius = getRadius() + ball.getRadius(); float sqrRadius = sumRadius * sumRadius; float distSqr = (xd * xd) + (yd * yd); if (distSqr <= sqrRadius) { return true; } return false; } public void resolveCollision(Ball ball) { // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); // impact speed Vector2d v = (this.velocity.subtract(ball.velocity)); float vn = v.dot(mtd.normalize()); // sphere intersecting but moving away from each other already if (vn > 0.0f) return; // collision impulse float i = (-(1.0f + Constants.restitution) * vn) / (im1 + im2); Vector2d impulse = mtd.multiply(i); // change in momentum this.velocity = this.velocity.add(impulse.multiply(im1)); ball.velocity = ball.velocity.subtract(impulse.multiply(im2)); } Source Code: Complete source for ball to ball collider. Binary: Compiled binary in case you just want to try bouncing some balls around. If anyone has some suggestions for how to improve this basic physics simulator let me know! One thing I have yet to add is angular momentum so the balls will roll more realistically. Any other suggestions? Leave a comment!

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  • Using CGRectIntersectsRect for collision detection

    - by user309030
    Hi guys, I've got a long rectangular image which is rotated at different kind of angles. However the frame of the rectangular image does not rotate along with the image and instead, the rotation causes the frame to to become larger to fit the rotated image. So when I used CGRectIntersectsRect, the collision detection is totally off because the other image colliding with the rectangular image will collide before it even reaches the visible area of the rect image. In case you don't really know what I'm talking about, have a look at the ascii drawing: normal rectangular image frame, O - pixels, |, – - frame |----------| |OOOOOOOOOO| |----------| after rotation |----------| |O | | O | | O | | O | | O | | O | | O | | O | | O | |----------| I've read through some of the collision articles but all of them are talking about collision with a normal straight rectangle and what I really want is collision with a slanted image, preferably pixel collision detection. TIA for any suggestions made.

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  • I need help with 2D collision response (of stacking rotating polygons, with friction and gravity, for a game)

    - by Register Sole
    Hi I am looking for suggestions on how to write a collision response for game programming purpose (so not a scientific simulation). I am dealing with 2D polygons that are rotating, and I want them to be able to stack. I also want friction and gravity. I have a detection mechanism that returns the separating axis, how long the polygons are overlapping, and up to 2 points of contact. For the response, I am currently using an impulse-based response, which main idea is: find the separating axis, length of overlap, and the point of contact (if there are two, pick a random point between to simulate averaged force. i believe there are better ways than this) separate the object (modifying their positions, taking into account of their masses. i do not separate them completely though, to keep track that they are colliding to reduce jitter) calculate normal force based on the coefficient of restitution as if there is no friction. calculate friction, as if there is no normal force. I also assume that the direction of the friction is the same throughout the collision. apply the two forces (which result in a rather inaccurate result, since each force is calculated as if the other is not present. for non-rotating bodies though, this method is exact) I am aware that this method requires the coefficient of friction to be sufficiently small due to the assumption that the direction of friction stays the same in a collision. Also, the result is visually satisfying if gravity is not present. However, when there is gravity, objects on ground jitter and drift (even with zero coefficient of restitution)! It also happens for stacking objects. Larger coefficient of restitution and gravity increase the jittering. I hope you can help me with this. Some things i would like to know more about is how to handle collision with two point of contacts (how to end up having an object sitting still on the ground?), how to reduce, and prevent if possible, jitter and drift (do people use the most accurate method possible, or is there a trick to overcome this?), and how to handle multiple objects collision (for example, in the case of stacking objects, how do I check collisions between all of them and keep them all stable at every frame so they don't jitter?). A total reformulation of my algorithm is also welcomed, as long as it works. Another thing to note is that I am not making a Physics game, so I only need a visually satisfying response (though a realistic response is preferable, if it is not performance-heavy). But surely jittering and drifting objects on flat ground are not at all acceptable. In addition, I am a Physics student, so feel free to talk about impulse and whatever needed. Finally, I'm sorry for the long post. I tried to be as concise as I can. Thank you for reading it! EDIT It seems what I didn't manage to come up all this time is to separate resting contact as a class of its own and how to solve them. Currently reading the paper suggested by Jedediah. More suggestions on the topic are welcome :) CASE CLOSED After reading various papers referenced in the paper, successfully implemented simultaneous impulse method (referring to the original paper by Erin Catto, [Catt05]). Thanks maaaan!! The paper is wonderful. The current system is visibly much better than the previous. Still haven't separated resting contact as a class of its own though, which brings me to my next question. Love you all! Haha (sorry, I'm just so happy thanks to you).

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  • Need help with implementing collision detection using the Separating Axis Theorem

    - by Eddie Ringle
    So, after hours of Googling and reading, I've found that the basic process of detecting a collision using SAT is: for each edge of poly A project A and B onto the normal for this edge if intervals do not overlap, return false end for for each edge of poly B project A and B onto the normal for this edge if intervals do not overlap, return false end for However, as many ways as I try to implement this in code, I just cannot get it to detect the collision. My current code is as follows: for (unsigned int i = 0; i < asteroids.size(); i++) { if (asteroids.valid(i)) { asteroids[i]->Update(); // Player-Asteroid collision detection bool collision = true; SDL_Rect asteroidBox = asteroids[i]->boundingBox; // Bullet-Asteroid collision detection for (unsigned int j = 0; j < player.bullets.size(); j++) { if (player.bullets.valid(j)) { Bullet b = player.bullets[j]; collision = true; if (b.x + (b.w / 2.0f) < asteroidBox.x - (asteroidBox.w / 2.0f)) collision = false; if (b.x - (b.w / 2.0f) > asteroidBox.x + (asteroidBox.w / 2.0f)) collision = false; if (b.y - (b.h / 2.0f) > asteroidBox.y + (asteroidBox.h / 2.0f)) collision = false; if (b.y + (b.h / 2.0f) < asteroidBox.y - (asteroidBox.h / 2.0f)) collision = false; if (collision) { bool realCollision = false; float min1, max1, min2, max2; // Create a list of vertices for the bullet CrissCross::Data::LList<Vector2D *> bullVerts; bullVerts.insert(new Vector2D(b.x - b.w / 2.0f, b.y + b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x - b.w / 2.0f, b.y - b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x + b.w / 2.0f, b.y - b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x + b.w / 2.0f, b.y + b.h / 2.0f)); // Create a list of vectors of the edges of the bullet and the asteroid CrissCross::Data::LList<Vector2D *> bullEdges; CrissCross::Data::LList<Vector2D *> asteroidEdges; for (int k = 0; k < 4; k++) { int n = (k == 3) ? 0 : k + 1; bullEdges.insert(new Vector2D(bullVerts[k]->x - bullVerts[n]->x, bullVerts[k]->y - bullVerts[n]->y)); asteroidEdges.insert(new Vector2D(asteroids[i]->vertices[k]->x - asteroids[i]->vertices[n]->x, asteroids[i]->vertices[k]->y - asteroids[i]->vertices[n]->y)); } for (unsigned int k = 0; k < asteroidEdges.size(); k++) { Vector2D *axis = asteroidEdges[k]->getPerpendicular(); min1 = max1 = axis->dotProduct(asteroids[i]->vertices[0]); for (unsigned int l = 1; l < asteroids[i]->vertices.size(); l++) { float test = axis->dotProduct(asteroids[i]->vertices[l]); min1 = (test < min1) ? test : min1; max1 = (test > max1) ? test : max1; } min2 = max2 = axis->dotProduct(bullVerts[0]); for (unsigned int l = 1; l < bullVerts.size(); l++) { float test = axis->dotProduct(bullVerts[l]); min2 = (test < min2) ? test : min2; max2 = (test > max2) ? test : max2; } delete axis; axis = NULL; if ( (min1 - max2) > 0 || (min2 - max1) > 0 ) { realCollision = false; break; } else { realCollision = true; } } if (realCollision == false) { for (unsigned int k = 0; k < bullEdges.size(); k++) { Vector2D *axis = bullEdges[k]->getPerpendicular(); min1 = max1 = axis->dotProduct(asteroids[i]->vertices[0]); for (unsigned int l = 1; l < asteroids[i]->vertices.size(); l++) { float test = axis->dotProduct(asteroids[i]->vertices[l]); min1 = (test < min1) ? test : min1; max1 = (test > max1) ? test : max1; } min2 = max2 = axis->dotProduct(bullVerts[0]); for (unsigned int l = 1; l < bullVerts.size(); l++) { float test = axis->dotProduct(bullVerts[l]); min2 = (test < min2) ? test : min2; max2 = (test > max2) ? test : max2; } delete axis; axis = NULL; if ( (min1 - max2) > 0 || (min2 - max1) > 0 ) { realCollision = false; break; } else { realCollision = true; } } } if (realCollision) { player.bullets.remove(j); int numAsteroids; float newDegree; srand ( j + asteroidBox.x ); if ( asteroids[i]->degree == 90.0f ) { if ( rand() % 2 == 1 ) { numAsteroids = 3; newDegree = 30.0f; } else { numAsteroids = 2; newDegree = 45.0f; } for ( int k = 0; k < numAsteroids; k++) asteroids.insert(new Asteroid(asteroidBox.x + (10 * k), asteroidBox.y + (10 * k), newDegree)); } delete asteroids[i]; asteroids.remove(i); } while (bullVerts.size()) { delete bullVerts[0]; bullVerts.remove(0); } while (bullEdges.size()) { delete bullEdges[0]; bullEdges.remove(0); } while (asteroidEdges.size()) { delete asteroidEdges[0]; asteroidEdges.remove(0); } } } } } } bullEdges is a list of vectors of the edges of a bullet, asteroidEdges is similar, and bullVerts and asteroids[i].vertices are, obviously, lists of vectors of each vertex for the respective bullet or asteroid. Honestly, I'm not looking for code corrections, just a fresh set of eyes.

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  • 2D Platformer Collision Problems With Both Axes

    - by AusGat
    I'm working on a little 2D platformer/fighting game with C++ and SDL, and I'm having quite a bit of trouble with the collision detection. The levels are made up of an array of tiles, and I use a for loop to go through each one (I know it may not be the best way to do it, and I may need help with that too). For each side of the character, I move it one pixel in that direction and check for a collision (I also check to see if the character is moving in that direction). If there is a collision, I set the velocity to 0 and move the player to the edge of the tile. My problem is that if I check for horizontal collisions first, and the player moves vertically at more than one pixel per frame, it handles the horizontal collision and moves the character to the side of the tile even if the tile is below (or above) the character. If I handle vertical collision first, it does the same, except it does it for the horizontal axis. How can I handle collisions on both axes without having those problems? Is there any better way to handle collision than how I'm doing it?

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  • How do I implement collision detection with a sprite walking up a rocky-terrain hill?

    - by detectivecalcite
    I'm working in SDL and have bounding rectangles for collisions set up for each frame of the sprite's animation. However, I recently stumbled upon the issue of putting together collisions for characters walking up and down hills/slopes with irregularly curved or rocky terrain - what's a good way to do collisions for that type of situation? Per-pixel? Loading up the points of the incline and doing player-line collision checking? Should I use bounding rectangles in general or circle collision detection?

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